Electrophotographic element which includes a photoconductive polyvinyl carbazole layer containing an aromatic anhydride

ABSTRACT

For use in an electrophotographic copy process, a photoconductive element comprising a support for an organic photoconductive coating comprising a polymerized vinyl carbazole, 2,4,7-trinitro-9-fluorenone and an aromatic anhydride present in amounts of about 0.49 to 1.23 moles of the trinitrofluorenone per monomeric unit of polyvinyl carbazole and 0.05 to 5.0 percent by weight of aromatic anhydride based upon the amount of polyvinyl carbazole.

United States Patent [191 Curtin [451 Dec. 23, 1975 ELECTROPHOTOGRAPHIC ELEMENT WHICH INCLUDES A PHOTOCONDUCTIVE POLYVINYL CARBAZOLE LAYER CONTAINING AN AROMATIC ANHYDRIDE [75] Inventor: Denis J. Curtin, Chicago, Ill.

[73] Assignee: A. B. Dick Company, Niles, Ill.

[22] Filed: June 7, 1974 [21] Appl. No.: 477,301

OTHER PUBLICATIONS Nepela et al., IBM Technical Disclosure Bulletin, Sensitization of Organic Photoconductor Complexes Using Quinones, Vol. 13, No. 5, Oct. 1970.

Primary ExaminerMary F. Kelley Assistant Examiner-Judson R. Hightower [57] ABSTRACT For use in an electrophotographic copy process, a photoconductive element comprising a support for an organic photoconductive coating comprising a polymerized vinyl carbazole, 2,4,7-trinitro-9-f1uorenone and an aromatic anhydride present in amounts of about 0.49 to 1.23 moles of the trinitrofluorenone per monomeric unit of polyvinyl carbazole and 0.05 to 5.0 percent by weight of aromatic anhydride based upon the amount of polyvinyl carbazole.

12 Claims, No Drawings ELECTROPHOTOGRAPHIC ELEMENT WHICH INCLUDES A PHOTOCONDUCTIVE POLYVINYL CARBAZOLE LAYER CONTAINING AN AROMATIC ANHYDRIDE This invention relates to photoconductors and more particularly to an organic photoconductor composition for use in the preparation of photoconductive elements in the production of copy by the electrophotographic process.

In the electrophotographic copy process, use is made of a photoconductive surface onto which a uniform electrostatic charge is applied. The charge is retained on the surface except for those areas that are rendered conductive during exposure to a light pattern, leaving a latent electrostatic image on the non-exposed portions of the photoconductive surface. The latent electrostatic image is subsequently developed in a conventional manner, as by means of a dry developing powder which is cascaded over the surface, or by a liquid developer or toner suspended in an insulating liquid with which the plate surface is wet. Instead, the latent electrostatic image can be transferred to a copy sheet for development of the image thereon, as by a liquid or powder developer.

To the present, especially in relatively high speed copy machines, amorphous selenium, with or without an added dopant, has been used to provide the photoconductive surface on a suitable support. While selenium provides a photoconductive surface having the desired speed and sensitivity for use in high speed copy machines, selenium represents a relatively expensive material which is difficult to apply, and its use as aphotoconductive composition is somewhat restricted to a support formed of a rigid material such as a metal drum or plate.

There is considerable interest in a low cost organic photoconductive composition which might be applied by conventional coating techniques, for use on various supports, such as on an endless belt, flexible paper, metal or plastic strip, and the like, as well as on a rigid metal drum or plate.

While organic photoconductors offer advantages of the type described, they are also faced with a number of disadvantages in that organic photoconductors, which have been suggested to the present, are characterized by low charge acceptance and lesser sensitivity by comparison with selenium.

In US. Pat. No. 3,484,237, description is made of an organic photoconductor composition formed of a polymerized vinyl carbazole compound to which 2,4,7- trinitro-9-fluorenone has been added as an electron acceptor to lower the dark conductivity of the photoconductive layer and to increase the sensitivity in the visible range.

It is an object of this invention to increase the photoconductivity, charge acceptance, and sensitivity of photoconductive compositions of the type described in the aforementioned U.S. Pat. No. 3,484,237, whereby the photoconductive element embodying the advantages available from the use of an organic photoconductor composition and the speed and sensitivity com parable to a photoconductor formed of selenium is obtained.

More specifically, it is an object of this invention to provide an organic photoconductor composition from which a photoconductor can be produced having good none (TNF) and a polymerized vinyl carbazole (PVK) 0 present in the ratio of about 0.49 to 1.3 moles of TNF per monomer unit of PVK can be improved when addition is made of an aromatic anhydride. By the addition of aromatic anhydride, the charge acceptance of the photoconductive layer can be increased by at least 25% and the sensitivity of the photoconductive coating can be increased three to eight fold or more with corresponding increase in copy speed by comparison with the same composition without the added aromatic anhydride. This represents a significant improvement whereby copy speed and quality suitable for high speed copy machines can be achieved.

Polymerized vinyl carbazole compounds suitable for' use in the photoconductive compositions of this invention are poly-N-vinyl carbazole and polyvinyl-N-lower alkyl carbazoles of the type described in the U.S. Pat. No. 3,484,237. The following can be given by way of examples of suitable poly-N-lower alkyl carbazoles, namely, poly-2-vinyl-N-methylcarbazole, poly-3-vinyl- N-ethylcarbazole, poly-2-vinyl-N-ethylcarbazole, poly- 3-vinyl-N-methylcarbazole, poly-3-vinyl-N-isopropylcarbazole, poly-2-vinyl-N-butylcarbazole, poly-3-vinyl- N-butylcarbazole, poly-2-vinyl-N-pentylcarbazole, poly-3-vinyl-N-pentylcarbazole, poly-2-vinyl-N-hexylcarbazole, poly-3-vinyl-N-hexylcarbazole, poly-2-vinyl- N-heptylcarbazole, and poly-3-vinyl-N-heptylcarbazole. Mixtures and copolymers of the polymerized vinyl-carbazole compounds also may be used.

Representative of the aromatic anhydrides which can be used in the "practice of the invention are phthalic anhydride (PA), l,2,4,5-benzene-tetracarboxylic anhydride (BT), mellitic trianhydride (MT), and the like anhydrides of dicarboxylic, tricarboxylic, tetracarboxylic and polycarboxylic benzyl, naphthyl, and anthracyl, or other unsubstituted or substituted aromatic ring structures. The desired improvements are experienced when the phthalic anhydride, mellitic trianhydride, l,2,4,5-benzene-tetracarboxylic anhydride, or other aromatic anhydrides is present in the photoconductive composition in an amount within the range of 0.05 to 5.0, and preferably 0.90 to 1.7 percent by weight of the polyvinylcarbazole component.

The materials are formulated into a composition for coating onto a suitable substrate by first dissolving the polyvinylcarbazole component in a suitable solvent, such as tetrahydrofuran, and then admixing the solution of the polyvinylcarbazole with the 2,4,7-trinitro-9- fluorenone and aromatic anhydride, preferably in solution in the same solvent, and any additional solvent required to achieve the desired consistency for the coating composition. The materials may be worked into solution on a roller mill and the like and coated on a suitable substrate, such as a aper plate, silicated aluminum plate, or the like, by conventional coating means, followed by air drying and thii curing at el= vated temperature such as for one hour at 50-60C.

Instead of tetrahydrofuran, other solvents such as 1,2-dichloroethane and chlorobenzene may be used.

The photoconductive compositions of the present invention are useful in the conventional xerographic process in which an electrostatic image is formed on the surface of the photoconductive element and the electrostatic image is subsequently developed. In practice, the photoconductive element is electrostatically charged and exposed to a pattern of light and dark to form an electrostatic image. Thereafter, the electrostatic image can either be developed with a conventional electroscopic powder developer on the photoconductive element and the developed image transferred to plain paper, or the electrostatic image can be transferred to a dielectric paper for development with an electroscopic developer (powder or liquid). The following examples will illustrate the improvement that is achieved by the addition of the aromatic anhydride to the organic photoconductor composition in accordance with the practice of this invention.

EXAMPLES l to 4 In the following examples, a photoconductive coating formulated of 2,4,7-trinitro-9-fluorenone (TNF) and poly-N-vinylcarbazole (PVK) in the amount described will be compared with coatings of the same composition but with the addition of the same amounts of various aromatic anhydrides, representative of the practice of this invention. Comparisons will be made from the standpoint of initial charge, and residual charge in volts, dark decay in volts per second, and sensitivity at light exposures of 7, l4 and 28 p. J/cm For this purpose, a master mix was prepared of 24.8 grams 2,4,7-trinitro-9-fluorenone from Aldrich Chemical Co. Inc., 575 ml tetrahydrofuran previously dried over sodium, 160 ml of 10% solution in tetrahydrofuran of poly-N-vinyl-carbazole from Ionac Chemical Company.

The solution of the above materials was divided into four equal segments, identified as Examples 1, 2, 3, and 4. In Example 1, no addition was made. In Example 2, 0.5 ml of 1% by weight solvent solution in tetrahydrofuran of phthalic anhydride was added. In Example 3, 0.5 ml of a 1% solution in tetrahydrofuran of 1,2,4,5-benzene-tetracarboxylic anhydride was added. In Example 4, addition was made of 0.5 ml of a 1% solution in tetrahydrofuran of mellitic anhydride.

The compositions of each of the four examples were milled on a roller immediately prior to coating. The compositions of Examples l-4 were each applied onto 3.5 mil silicated aluminum substrate with a Paasche H-5 artist air brush. For this purpose, the aluminum plate was mounted onto a drum supported for rotational movement about a horizontal axis. The air brush was attached to a rack and pinion mechanism which allowed the air brush to be moved across the width of the plate at a fixed plate surface to air brush distance.

During rotation of the drum at about 13 rpm, a narrow strip of coating was applied bythe air brush, using nitrogen gas. After each rotation, the air brush was moved about 2 mm and another strip was applied until the aluminum plate was covered with a thin coating to a coating thickness of 5-20 microns, and preferably 8-15 microns. The plates were allowed to air dry and then the coating was cured for 60 minutes at 50C.

The plates were subjected to tests for acceptance and retention of electrostatic charge, including charge decay in the dark. For this purpose, the plates were each exposed to a negative electrostatic corona charge of 6 KV .by passing the plate beneath charging wires and the charged plates were tested for initial voltage, residual charge, dark decay and sensitivity. Initial charge, charge retention and charge acceptance were measured by a Monroe electrometer which measures the charge on the surface of the plate. Dark decay was calculated by the rate of charge loss per second. Sensitivity was determined by the Monroe electrometer to calculate the amount of charge dissipated by light upon exposure. Exposure was made with a tungsten photo enlarger lamp 150 W) operating through an enlarger. Energy of exposure identifies the amount of light that fell on the plate p. J/cm as measured by a Hewlett-Packard radiant flux meter.

TABLE I Initial Residual Dark charge charge decay Example Additive (V) (V) (V/sec) 1 None 24 2.2 2 Phthalic anhydride 300 30 3.3 3 l,2,4,5-benzene- 500 30 1.5

tetracarboxylic anhydride 4 Mellitic anhydride 600 30 3.3

' TABLE II Exposure Average =Percent Example 14 28 sensitivlty Improvement sensitivity 1 4.0 3.3 2.5 3.3 2 12.9 10.0 7.1 10.0 303, 3 22.9 15.6 12.9 18.1 548 4 28.6 23.2 16.1 26.6 806 From the results on sensitivity, it will be seen that the additions of aromatic anhydrides resulted in a three to eight fold increase in the sensitivity of the photoconductor, permitting a three to eight fold increase in speed. This corresponds to a reduction in copy time for the photoconductor with the added aromatic anhydride when compared to a photoconductor of the same composition without added aromatio anhydride. This marked increase in light sensitivity of the photoconductor composition permits the elimination of activator, such as the undesirable dyestuffs heretofore employed in compositions of the type described, without loss of copy speed or copy quality.

The following are further examples of the practice of this invention with various aromatic anhydrides added to the system of 2,4,7-trinitro-9-fluorenone and poly- N-vinyl-carbazole in varying amount.

EXAMPLE 5 6.2 grams TNF 40.0 ml of 10% poly-N-vinylcarbazole in tetrahydrofuran (THF) 600ml THF 5.0 ml of a 1% solution of phthalic anhydride in THF EXAMPLE 6 grams TNF 100 ml THF 65 ml of 10% solution of poly-N-vinylcarbazole in THF 4.8 ml of a 1% solution of phthalic anhydride in THF EXAMPLE 7 6.2 grams TNF 40.0 ml of 10% solution of poly-N-vinylcarbazole in THF 60.0 ml THE 0.5 ml of a 1% solution of BT in THF EXAMPLE 8 6.2 grams of TNF 60.0 ml THF 40.0 ml 10% solution of polyN-vinylcarbazole in THF 0.5 ml of a 1% solution of MT in THF The formulations of Examples 5 to 8 were roller milled until the material became dissolved in the THF. The milled compositions were each coated on a substrate in the form of a silicated aluminum plate having a thickness of 0.0035 inch. The photoconductive coating compositions of Examples 5 to 8 were applied by the meniscus coating method in coating thickness of 5-20 microns, and preferably 8-15 microns. The coated plates were allowed to air dry and then cured for one hour at 60C.

The following is a tabulation comparing the electrical properties of the plates prepared in Examples 5 to 8, compared with a plate prepared in the same way, with a similar photoconductor composition, but without the added aromatic anhydride:

TABLE 111 The plates of Example 6 were imaged by cascading a commercial IBM powder developer over the surface of the imaged plate. The toned image was transferred to bond paper by the use of a negative corona, in accordance with conventional practice, and then exposed to an [R lamp for a time sufficient to heat the toner particles to fusion to set the image. Copy of good quality was secured in times corresponding to that experienced in commercial practice with selenium plates.

It will be understood that changes may be made in the details of formulation and operation, without de- 6 parting from the spirit of the invention, especially as defined by the following claims.

1 claim:

1. An electrophotographic element for use in an electrophotographic copy process comprising a substrate having a photoconductive coating on one surface of the substrate comprising 2,4,7-trinitro-9-fluorenone, a polyvinylcarbazole, and an aromatic anhydride in which the materials are present in the composition of which the coating is formed in the ratio of about 0.49 to 1.23 moles of the 2,4,7-trinitro-9-fluorenone per m0- nomeric unit of the polyvinylcarbazole, and 0.05 to 5.0 parts by weight of the aromatic anhydride per parts by weight of the polyvinylcarbazole.

2. An electrophotographic element as claimed in claim 1 in which the aromatic anhydride is present in an amount within the range of 0.90 to 1.7 parts by weight per 100 parts by weight of the polyvinylcarbazole.

3. An electrophotographic element as claimed in claim 1 in which the polyvinylcarbazole is poly-N-vinylcarbazole.

4. An electrophotographic element as claimed in claim 1 in which the aromatic anhydride is phthalic anhydride.

5. An electrophotographic element as claimed in claim 1 in which the aromatic anhydride is 1,2,4,5-benzene-tetracarboxylic anhydride (BT).

6. An electrophotographic element as claimed in claim 1 in which the aromatic anhydride is mellitic trianhydride (MT).

7. An organic photoconductive composition for use in the preparation of a photoconductive coating from which copies can be produced by an electrophotographic process, in which the composition consists essentially of an organic solvent solution of 2,4,7-trinitrofluorenone, a polyvinylcarbazole and an aromatic anhydride in which the materials are present in the solvent solution in the ratio of about 0.49 to 1.23 moles of the trinitrofluorenone per monomeric unit of the polyvinylcarbazole, and 0.05 to 5.0 parts by weight of the aromatic anhydride per 100 parts by weight of the polyvinyl-carbazole.

8. An organic photoconductive composition as claimed in claim 7 in which the aromatic anhydride is present in an amount within the range of 0.90 to 1.7 parts by weight per 100 parts by weight of the polyvinylcarbazole.

9. An organic photoconductive composition as claimed in claim 7 in which the polyvinylcarbazole is poly-N-vinylcarbazole.

10. An organic photoconductive composition as claimed in claim 7 in which the aromatic anhydride is phthalic anhydride.

11. An organic photoconductive composition as claimed in claim 7 in which the aromatic anhydride is 1,2,4,5-benzene-tetracarboxylic anhydride (BT).

12. An organic photoconductive composition as claimed in claim 7 in which the aromatic anhydride is mellitic trianhydride (MT). 

1. AN ELECTROPHOTOGRAPHIC ELEMENT FOR USE IN AN ELECTROPHOTOGRAPHIC COMP PROCESS COMPRISING A SUBSTRATE HAVING A PHOTOCONDUCTIVE COATING ON ONE SURFACE OF THE SUBSTRATE COMPRISING 2,4,7-TRINITRO-9-FLUORENONE, A POLYVINYLCARBOZOLE, AND AN AROMATIC ANHYDRIDE IN WHICH THE MATERIALS ARE PRESENT IN THE COMPOSITION OF WHICH THE COATING IS FORMED IN THE RATIO OF ABOUT 0.49 TO 1.23 MOLES OF THE 2,4,7-TRINITRO-9-FLUORENONE PER MONOMERIC UNIT OF THE POLYVINYLVARBAZOLE AND 0.05 TO 5.0 PARTS BY WEIGHT OF THE AROMATIC ANHYDRIDE PER 100 PARTS BY WEIGHT OF THE POLYVINYLCARBAZOLE.
 2. An electrophotographic element as claimed in claim 1 in which the aromatic anhydride is present in an amount within the range of 0.90 to 1.7 parts by weight per 100 parts by weight of the polyvinylcarbazole.
 3. An electrophotographic element as claimed in claim 1 in which the polyvinylcarbazole is poly-N-vinylcarbazole.
 4. An electrophotographic element as claimed in claim 1 in which the aromatic anhydride is phthalic anhydride.
 5. An electrophotographic element as claimed in claim 1 in which the aromatic anhydride is 1,2,4,5-benzene-tetracarboxylic anhydride (BT).
 6. An electrophotographic element as claimed in claim 1 in which the aromatic anhydride is mellitic trianhydride (MT).
 7. An organic photoconductive composition for use in the preparation of a photoconductive coating from which copies can be produced by an electrophotographic process, in which the composition consists essentially of an organic solvent solution of 2,4,7-trinitrofluorenone, a polyvinylcarbazole and an aromatic anhydride in which the materials are present in the solvent solution in the ratio of about 0.49 to 1.23 moles of the trinitrofluorenone per monomeric unit of the polyvinylcarbazole, and 0.05 to 5.0 parts by weight of the aromatic anhydride per 100 parts by weight of the polyvinyl-carbazole.
 8. An organic photoconductive composition as claimed in claim 7 in which the aromatic anhydride is present in an amount within the range of 0.90 to 1.7 parts by weight per 100 parts by weight of the polyvinylcarbazole.
 9. An organic photoconductive composition as claimed in claim 7 in which the polyvinylcarbazole is poly-N-vinylcarbazole.
 10. An organic photoconductive composition as claimed in claim 7 in which the aromatic anhydride is phthalic anhydride.
 11. An organic photoconductive composition as claimed in claim 7 in which the aromatic anhydride is 1,2,4,5-benzene-tetracarboxylic anhydride (BT).
 12. An organic photoconductive composition as claimed in claim 7 in which the aromatic anhydride is mellitic trianhydride (MT). 